Simplification is the order of the day: What is behind the different types of exposure metering – matrix/multi/multi-segment metering, spot metering, center-weighted metering? The differences can be summarized briefly, and with this background knowledge you can decide for yourself when which method makes sense.
The different types of exposure metering differ in
With low-contrast subjects, the brightness being about the same everywhere in the image, all metering methods produce the same result.
These are the terms used by Canon, Nikon, Sony and Fuji for their preset exposure metering, which is supposed to deliver good results automatically in as many different situations as possible. Like Sony, I call it ”multi metering“ here as this fits best the common aspect – measuring subject brightness in many different segments of the image.
I chose the example photo because of high brightness contrasts of the sky and the trees lying in the shade. It is taken with Nikon's matrix metering, but the explanations fit all manufacturers.
Multi-segment metering measures the subject brightness in many segments across almost the entire image, hence the blue frame in the next picture. SLR cameras have separate sensors for measuring exposure with hundreds or even several thousand metering segments. Mirrorless cameras measure directly on the image sensor. With all these measured values, the camera uses a complex logic to determine an average exposure – but how exactly this works is not documented by the manufacturers. The only thing that is certain is that the procedures have become more sophisticated and complex over time.
Due to the measurement in many places, the camera can e.g.
Modern cameras analyse the subject in real time before the picture is taken in order to recognise faces, for example, and adjust the exposure accordingly. Smartphones, which have more sophisticated internal image processing, go further than conventional cameras.
In the example photo, however, the multi metering has produced small overexposed areas in the sky; I don't like these, would like the sky to have more contrast, and also think that the image would look better with a slightly darker appearance. In the example, that would bring me to a photo with exposure compensation -1.0.
Nevertheless, multi-field metering is a sensible choice and suitable for the vast majority of situations. It works well, even many professionals use it. It automatically finds a suitable exposure more often than the other metering methods.
On the other hand, you don't always know where exactly the camera has determined the brightness and how. Those who want to control the exposure themselves may feel more comfortable with the other methods, as they require more thinking, but work more predictably.
Cameras always use multi-segment metering when shooting with full auto and as the default setting in all other camera modes unless you actively set a different metering method.
Spot metering measures the brightness in a small circle and ignores all the rest. The circle for metering can be in the centre or follow the autofocus, depending on the camera model and possibly camera settings. If you are lucky, your camera will display the circle for spot metering.
Nikon and Canon cameras state that spot metering uses ”about 1.5% of the viewfinder area“. This corresponds to a circle with a diameter of 1/6 of the image height or 1/9 of the image width.
It may be that the size of the circle for spot metering differs on individual camera models or is adjustable in size. Canon, for example, offers ”partial metering“ for this purpose, which is simply spot metering with a slightly larger metering circle, about 1/3 of the image height.
The next image shows this small measuring spot and what is the result in the chosen example – a much brighter image, because the small spot was exactly on a dark tree. Spot metering is for snipers who use it to target exactly one spot in the image, otherwise the results are rather random.
Here's the comparison: panned the camera just slightly so that the spot area is pointing at the bright sky, pressed the exposure lock button to fix the exposure, and panned the camera back. Because of the metering at a much brighter subject spot, the image turns out so much darker.
Spot metering is advisable if you
It is a good idea to use the spot metering together with the exposure lock, then you can first measure an arbitrary area and then finish the image section at your leisure. It is difficult to do both at the same time, because with spot metering a small change in the targeted spot causes significant changes in exposure.
In addition, spots that should turn white in the photo need positive exposure compensation, and conversely black spots need negative exposure compensation – as explained on the Understanding exposure metering page.
The exposure metering is performed across the entire image, but weights a circle in the center more heavily. The size of the circle is about half the height of the image, but again, camera models may differ or offer a setting for this value. This type of metering has existed for decades and has persisted to this day.
Center-weighted metering is useful when you want to have full control over exposure, especially in conjunction with exposure lock. In contrast to multi-segment metering, you reliably know in which image area the camera determines the exposure.
Also in centre-weighted metering, predominantly bright subjects can additionally take a positive, dark subjects a negative exposure compensation. However, the larger measuring range compared to spot metering will usually ensure a sufficient mixture of bright and dark areas.
That's how it was here, by the way; I don't show a comparison picture with the centre-weighted measurement because it gave the same result as the multi-field measurement. And in order to achieve the result I wanted with the centre-weighted metering, as shown above, I would have
Result: Exactly as above, when I used -1.0 exposure compensation for the multi-field metering. It is a matter of experience which exact compensation to use and normal that you try different values, I do the same.
Before moving on to the next method, a quick step back to what we have seen so far:
It may seem confusing at first glance, but the two rules from Understanding exposure metering and knowing where the different exposure metering methods look is all you need. And:
This type of exposure metering is based on the brightest areas in the picture and aims to avoid overexposing them.
Nikon calls it ”highlight-weighted metering“ , Sony "highlight" and I have not yet seen it (yet) at Canon.
The light-emphasised metering makes sense when
The example photo under the headline was taken with the highlight-weighted metering of a Nikon camera, now comes a second one with a slightly different image detail and matrix metering. The difference is one exposure stop, the images are JPGs from the camera, only slightly straightened and cropped. Click on them for a larger view, you can see how the sky is less saturated and the foreground is brighter.
Highlight-weighted metering becomes even more attractive if you edit your pictures afterwards. Then you definitely have the advantage of better recognisable bright parts of the image and can lighten the darker shadows. Even better in RAW than JPG, but that's another topic.
This is a variant of spot metering that I have only seen on smartphones so far: A tap in the picture preview causes a light metering exactly there. Just try it out, it works on most smartphones and the preview becomes brighter or darker when you tap on different bright spots in the picture.
This is of course also conceivable with pure cameras with touchscreens, but I haven't come across it yet. Please check for yourself how your camera behaves; probably only the focus can be controlled by tapping the touch screen, not the exposure.
How to set the metering depends on the camera – I can only give you a few hints on what to look for on your camera. If this does not help, please consult the manual of your camera.
The metering mode cannot be changed when shooting with full auto, the camera mode must be one for advanced shooting (P, S/Tv, A/Av, M or one for self-selected favorite settings).